What is this adapter on my Dallmeyer Pentac 2.9/8" for?

[schlicksbier]

I got today a Dallmeyer Pentac 2.9/8“ and was very surprised by the huge adapter on the lens. Any idea for what this brass adapter was used? The mount at the end is approx 5cm in diameter.

228235

228236

228237

[Steven Tribe]

Once upon a time (post WW2) there was a shortage of affordable lenses for, especially, 35mm cameras, but a lot of cheap fast ex military large format lenses were available.
So lots of people got adapters made to use these on prewar 35mm cameras. Lathe work with brass/aluminum tubing used to be readily available and low cost!

[schlicksbier]

Once upon a time (post WW2) there was a shortage of affordable lenses for, especially, 35mm cameras, but a lot of cheap fast ex military large format lenses were available.
So lots of people got adapters made to use these on prewar 35mm cameras. Lathe work with brass/aluminum tubing used to be readily available and low cost!

So they used this to attach it on some kind of helicoid to focus it correctly?

[domaz]

So they used this to attach it on some kind of helicoid to focus it correctly?

Or maybe it was just fixed focus at infinity, a poor man's telephoto for a 35mm camera.

[LabRat]

I have seen surplus lenses with that mount, and I think some old cinema projection lenses had them...

A Pentac is fast enough for projection...

Steve K